A recent significant advance in the burner art is the aspirator burner and combustion method developed by Dr. J. E. Anderson and described and claimed in U.S. Pat. Nos. 4,378,205 and 4,541,796. By means of this aspirator burner and process one can advantageously employ oxygen enriched air and even pure oxygen as the oxidant with resulting significantly improved operating efficiencies. The invention is characterized by a large radial distance between the fuel and oxidant injection points, said distance being at least four oxidant injection jet diameters, and is further characterized by a relatively high ratio of oxidant stream velocity to fuel stream velocity. Because of the large distance between the fuel and oxidant it is often desirable to provide a small amount of oxidant to the fuel as it enters the combustion zone to establish a flame front and thus have stable combustion.
The Anderson burner and combustion method enables the effective use of oxygen or oxygen-enriched air as the combustion oxidant while avoiding the very high heat associated with such combustion. This reduces both the furnace wear and the formation of nitrogen oxides, commonly referred to as NO.sub.x. The heat reduction and dissipation is accomplished by the high oxidant velocity and the large distance between the oxidant and fuel injection points. The high oxidant velocity causes furnace gases to be aspirated into the oxidant stream at a high rate and the large distance enables this aspiration to continue for a considerable time before the oxidant and fuel meet and combust. The aspirated gases dilute and add momentum to the combustion reaction thus spreading it out and keeping spot temperatures from increasing to an unacceptable level.
A difficulty with this aspirator burner and method is that at higher average furnace temperatures and at higher firing rates, a greater spacing between the oxidant and fuel jets may be necessary to keep NOx production low, especially if the oxidant is less than 100 percent oxygen, i.e., contains some nitrogen.
Accordingly it is an object of this invention to provide an improved aspirating combustion method wherein NO.sub.x formation is reduced.
It is a further object of this invention to provide an improved aspirating combustion method employing oxidant which may contain some nitrogen while achieving reduced NO.sub.x formation.